1. Field of the Invention
The invention relates to a process for removing dust particles from a web surface without contact, as well as a dedusting device for accomplishing the process.
2. Related Art
The designs of dedusting systems for moving material webs, also referred to as web-cleaning systems, can be roughly divided into those that operate without contact and those that operate with brush support. In the latter dedusting systems, the dust particles were mechanically removed from the material web with rotating brushing rollers or rows of stationary brushes and then suctioned off. The composition of the brushes, as well as their strength, material, and bristle design were matched in this case to the properties of the material surface that was to be cleaned. Such non-generic dedusting systems are described in Bundesverband Druck e.V. Federal Registered Association of Pressure!, P.O. Box 1869, Biebricher Allee 79, D - 6200 Wiesbaden 1, "Technischer Informationsdienst Technical Information Services!," II/1985, pp. 1 to 20, as well as in WO87/06527.
Dedusting systems that operated without contact had an injection unit, which directed a gas jet onto the web to be cleaned, as well as a suctioning unit, with which the gas that picked up the dust particles was suctioned off in turn. To discharge the dust particles that were found on the material web, discharge electrodes were arranged together with the injection unit or near it. Such dedusting systems are known from EP-A 0 245 526, EP-A 0 520 145, EP-A 0 524 415, EP-A 0 395 864 and CH-A 649 725.
Another approach was used in EP-A 0 084 633. Here, a turbulent flow of gas was directed toward a fabric web that was to be dedusted, and the latter was made to vibrate by the turbulent flow, causing the dust particles to be removed from the surface of the fabric. It was possible to use this type of dedusting only in the case of thin material webs, however, that could be made to vibrate by the gas jet.
A non-generic cleaning system for removing a liquid adhering to a moving belt, especially a rolling belt, is described in DE-A 4 215 602. The problems that arise in the case of a dedusting system with particles that adhere to the surface owing to electrostatic forces did not occur here.
To the extent that a fluidic configuration of the nozzle outlets of the injection units was implemented in the above-indicated dedusting systems, they were designed as channels that were inclined toward the material web with a constant channel cross-section in the area of the nozzle opening, as depicted in, e.g., EP-A 0 245 526, EP-A 0 520 145 and DE-A 4 214 602. Only in EP-A 0 084 633 and in an embodiment variant of DE-A 4 215 602 was an exhaust port cross-section of the nozzle with a variable cross-section described. In EP-A 0 084 633, the flow of gas was directed perpendicularly to the fabric web. In DE-A 4 215 602, a nozzle that was inaccurately referred to as a Laval nozzle was used with a cross-section which, after a narrowing, widens in a pear shape and then narrows again.
The invention achieves the object of ensuring the dedusting of a moving, stable material web that is not to be made to vibrate for dedusting, in which discharge electrodes are unnecessary.